Injection-moulding device

ABSTRACT

The invention relates to an injection-moulding device for injection moulding of plastic objects, having a mould which defines a mould cavity, in which mould is provided a flow channel for the at least partially liquid plastic, which flow channel extends through a manifold and a number of nozzles connected to the manifold, wherein the flow channel contains a number of transverse separating surfaces between structural components, and at least one transverse separating surface is bridged by a sealing element in the flow channel, which sealing element is provided clampingly on the structural components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an injection-moulding device.

2. Description of the Related Art

These injection-moulding devices are also referred to in the art as hotrunners, wherein the flow channel for the plastic melt in the device isheld at process temperature, whereby the plastic present in the mouldcan be re-used for a subsequent production cycle. The flow channel isgenerally embodied in metal and equipped with heating elements andthermocouples, wherein control equipment is present to set a suitabletemperature.

A critical component in such injection-moulding devices are the seals. Aknown seal is formed by a sealing ring which is enclosed with asufficiently large bias between two parallel surfaces. The ring can beeither solid or hollow, wherein the hollow ring has the advantage thatliquid plastic will flow into the ring and will contribute toward thesealing action. In such a known seal both the parallel surfaces are atright angles to the channel. The plastic pressure will then press apartboth the structural parts of which the sealing surfaces form part. Thebias of the ring must therefore be at least as great as the occurringplastic pressure times the projected area of the channel for sealing.This sealing action will be adversely affected by possible movements ofthe structural parts in axial direction relative to each other.

Such hot runners are moreover subject to considerable pressures of up to2000 bar and temperatures of about 480° C. This makes considerably moredifficult the sealing action for transverse separating surfaces in theflow channel. These transverse separating surfaces are for instancepresent between the manifold and the nozzles connected to the manifoldand between parts of the nozzles themselves.

Known from DE 43 24 027 is a sealing ring for bridging transverseseparating surfaces between modular components of an injection-mouldingdevice. This known injection-moulding device is applied for theinjection moulding of elastomeric objects, wherein wholly differentoperating conditions occur than in the case of hot runners. Theoperating temperature is for instance considerably lower.

BRIEF SUMMARY OF THE INVENTION

The invention has for its object to obviate the above stated drawback inhot runners and provides for this purpose an injection-moulding deviceas according to claim 1. By arranging a sealing element clampingly inthe flow channel a sealing is obtained of the surface which isconcentric to the flow channel.

The sealing element is preferably provided on the structural componentswith shrink fit in the diameter and optionally an overmeasure in thedimension in axial direction. In the case of a shrink fit the sealingelement is arranged in the flow channel with an overmeasure in thediameter while temperature is decreased, for instance with nitrogen. Arelatively large bias can be obtained with shrink fitting. When anovermeasure in the dimension in axial direction is also applied, asealing action is obtained in the case of two mutually perpendicularsurfaces.

Since the seal parallel to the flow channel is more critical thantransversely thereof, the sealing element is preferably formed by acylindrical bush, wherein the ratio of the diameter of the flow channel,wall thickness of the bush and height of the bush equals 22:2:10. Theplastic pressure will press the thin-walled bush against the wall of theflow channel. The higher the plastic pressure, the better the sealingaction will be. Should both structural components move axially or rotaterelative to each other, the sealing capacity will not then be affected,or only slightly.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The invention will be better understood in the light of the detaileddescription given below of a number of preferred embodiments withreference to the annexed drawing. Herein:

FIG. 1 shows a perspective, partly broken away view of a detail of aninjection-moulding device according to the invention;

FIGS. 2, 3 and 4 show enlarged perspective views of the sectors II, IIIand IV of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a broken-away mould 1 of an injection-moulding deviceaccording to the invention in which a manifold 2 runs out onto a nozzle3. A flow channel 4 extends through manifold 2 and nozzle 3. The flowchannel 4 for a plastic melt forms an angle with nozzle 3. Such a flowchannel 4 has a number of transverse separating surfaces 5, 5′ for whicha seal must be provided. The transverse separating surface 5 is presentbetween manifold 2 and nozzle 3, the transverse separating surface 5′ ispresent between components of the nozzle 3 itself.

The seal 6 between the structural components, manifold 2 and nozzle 3 iselucidated in the detail view of FIG. 4. A sealing element 6 is providedin flow channel 4 and is formed by a thin-walled bush which is placedwith shrink fitting in two cylindrical recesses 7, 8 arranged in nozzle3 and manifold 2. The passage of flow channel 4 hereby remains constant.

Seal 6 is arranged such that the plastic pressure in the flow channelwill press the thin-walled bush with its back against the cylindricalrecesses 7, 8 of the two structural parts 2, 3, thereby reinforcing thesealing action. Seal 6 extends over the contact surfaces between the twostructural parts. The higher the plastic pressure, the better thesealing action will be. If both components move slightly relative toeach other (axially or rotation), the sealing function will still bemaintained. The sealing surfaces are preferably concentric to flowchannel 4.

Seal 6 should preferably be made from a high chromium content steelalloy in order to keep the tensile strength as low as possible so as tofacilitate deformation of the bush. In order to avoid scoring, a hardsurface layer will preferably have to be applied. At a channel diameterof for instance 22 mm, the wall thickness of the bush will be roughly 2mm and the height about 10 mm. At other channel diameters thesedimensions will also change proportionally. In addition, the sealingbush preferably has an over measure in its height of 0.4 to 1.0% and isplaced for instance with a shrink fit of H7p6 (NEN 2807) in the flowchannel.

The shown device is provided in this transverse separating surface 5with an additional, independently acting seal 9. Should the first sealfail, the second seal will then take over its function. The hollowsealing rings 9 are provided for this purpose.

An injection-moulding device is assembled in mould 1 when the two havethe same temperature. Once in production, the injection-moulding devicewill be about 200° C. hotter than mould 1. The injection-moulding devicewill expand relative to mould 1. In the case of a manifold 2 with alength of 1000 mm, this will be about 3 mm. The thickness of themanifold will however also become greater, as will the length of nozzles3.

Two known techniques are currently used to provide space for thisexpansion, i.e. the sliding construction and the screwed construction.

The drawbacks of the sliding construction are: A danger with the slidingconstruction is that the sealing between the nozzle and the manifoldonly comes about at process temperature. Assembly will therefore have totake place very precisely (accurate to hundredths of millimeters).

In order to realize the bias, heavy structural parts are necessarybetween injection-moulding device and mould. This has the result thatmuch energy is lost in the form of heat and that cold locations arecreated in the injection-moulding device.

An injection-moulding device based on a sliding construction cannot besupplied as a fully finished system. The nozzles are not connectedfixedly to the manifold. Wiring of the system will not therefore becarried out by the injection-moulding device supplier. This saves costwhich will be manifest in the ordering price.

The screw method is applied, if possible. Owing to the expansion of themanifold the upper end of the nozzle will be moved along. The lower endis held in the mould and will thus remain in position. The nozzle isthus forced to bend. Note that these can be tubes with an outer diameterof 42 mm and a wall thickness of 10 mm. There are therefore limitationsto this method. If this method cannot be applied, recourse is had to thesliding method.

The drawbacks of the screwed construction are: It frequently occurs thata plastic product is formed which has a specifically formed surface atthe position of the gate. This means that the outflow opening must bemodified to the form of the product. In the case of a repair where thenozzle is disassembled, it is not possible in the screwed constructionto re-place the outflow opening in precisely the same position. It issuddenly found that components can be tightened just a little further.

In order to counter this a construction is available wherein use is madeof a wing nut providing the connection between the nozzle and themanifold. This solves the problem at this location. The problem persistshowever in the case of the screw outflow opening.

Another drawback is that the nominal screw thread diameter becomes verylarge. Screw tightening of the nozzle or of the wing nut wherein thecorrect bias is realized is difficult to perform in practice because therequired tightening moment is very great. Disassembly is consequentlyvery difficult. The danger of scoring of the screw thread is alwayspresent.

The component with outflow opening (gate insert) is fixedly connected tothe nozzle. The manifold is fixed in the mould. This means that in thecase of thermal expansion of the nozzle the gate insert will bedisplaced in axial direction in the mould. In order to realize thecorrect thermal properties in the outflow opening constrictions arearranged in the component. Failure of the gate insert at the position ofthe constriction is a regular occurrence as a consequence of the highfriction forces between insert and mould.

It is possible to point to a further reason why these gate insertsbreak. The lateral forces which ensure that the nozzle really does bendmust be transmitted by the mould via the insert to the nozzle. Thestresses at the position of the constriction in the gate insert willthereby become high. These are increased even further because theinsert, as a result of the bending of the nozzle, will also have to bend(in opposing direction). This will of course take place at the positionof the constriction.

These drawbacks are at least partly obviated by the device as in thepresent invention where the structural components defining thetransverse separating surface are formed by the manifold and nozzle, orwhere the nozzle is mounted on the manifold by means of a number ofindependently controllable connecting elements, or where a connectingplate is formed by a nut and bolt assembly.

The connection between manifold 2 and nozzle 3 is obtained with two, andpreferably four independently controllable connecting elements. In thedrawings 1 and 4 these take the form of a nut and bolt 10 assembly,wherein the nut is preferably formed by a clamp plate 11. Bolts 10extend through an opening provided for this purpose in manifold 2,screwed into the clamping plate 11 on the opposite side of the manifold2. The clamping plates 11 in turn engage the shoulder part 28 of nozzle3, whereby nozzle 3 is clamped fixedly against manifold 2.

The advantages hereof are that after disassembly the nozzle can bere-placed in exactly the same position, the tightening moments for thebolts are reasonable whereby assembly and disassembly will be simple torealize, and that due to their small size bolts and clamp plates can bereadily and cheaply provided with an anti-scoring layer. A particularform of the connection between manifold 2 and nozzle 3 is the use of anadaptor nozzle.

When a short nozzle is mounted on the end of a long manifold, theproposed upgraded construction with bolts and clamp plates will notperform better than the known constructions. The proposed improvementshown hereinafter is the specific solution to this problem. At theheight of the position of the nozzle a short adaptor nozzle is mountedtransversely on top of the manifold. The connection is made such that asmall angular displacement is possible between the two structuralcomponents.

When the manifold expands and the short nozzle is held in its position,the adaptor nozzle will assume a different angle relative to themanifold. The distance over which the nozzle is urged toward themanifold as a consequence of this rotation is compensated by the thermalexpansion of the adaptor nozzle. In this way there will be nodestructive forces present in the construction.

FIG. 2 shows in detail the gate 13 of nozzle 3 which debouches into themould cavity 12.

Provided centrally in flow channel 4 is a torpedo 14 which is coupled bymeans of three spokes 37 to the intermediate wall part 14′ of theforemost nozzle part 16 in order to facilitate the heat transport towardtorpedo 14 and gate 13.

A wedge-shaped sleeve 15 extends over the expansion space 36 in arecess, whereby blind areas are avoided in which plastic material canpossibly result in blockages.

The mutually coupled assembly of components 14, 37 and 14′ lies mounteddisplaceably in longitudinal direction of flow channel 4. This assemblywill slide forward (to the left in the drawing) against mould 1 oragainst a component (not shown) mounted in mould 1. This displacementforce is generated by the loss of pressure in the flow injection overthis assembly.

Nozzle 3 comprises a number of transverse structural components 16, 17mutually separated by a transverse separating surface 5′. The sealingbetween components 16 and 17 is likewise formed by a sealing element orsealing ring 18 which extends over transverse separating surface 5′.Sealing ring 18 lies in the corresponding recesses 29 and 30. A screw-inis applied to fixedly connect nozzle parts 16, 17. A known problem inthe prior art which occurs here is that the mutual positioning is notpredictable, which generally results in problems.

The connection of these two parts 16, 17 is realized according to theinvention by means of two semi-circular clamping plates 19 for enclosingthe outer periphery of nozzle parts 16, 17. Openings 31 are provided inthis clamping plate 19 for screwing thereof against the other clampingplate 19. The outer periphery of the nozzle parts is preferably providedwith a stepped portion 20, wherein clamping plate 19 comprises acorresponding recess 21. The inner side is preferably provided with twochamfered surfaces 33. These surfaces coincide with the incliningsurfaces on the two parts for mutual connection. When the semi-circularplates 19 are pulled toward each other by means of for instance bolts32, both nozzle parts 16, 17 will be pressed toward each other andassume a permanent fixed position.

Reference number 34 represents a fixation element that connects to theforemost nozzle part 16, as illustrated in FIG. 2. Reference number 38represents a cavity defined by a distal part of nozzle 3. The cavity 38extends about the fixation element 34. Reference number 39 represents acavity formed by the fixation element 34 and extends about the nozzlepart 16. Additionally, as shown in FIG. 1, the fixation element 34 makescontact with nozzle 3 on the larger outer diameter. In this way, theoutflow opening of the cavity 38 is kept in line with the mould cavity12 in spite of the thermal expansion of manifold 2, which causes thenozzle parts 16 and 17 to move radially with respect to their commonaxes. Thereby, in case of a possible leakage of plastic flowing tocavity 38, fixation element 34 ensures that plastic will not flowfurther than the point of contact between the fixation element 34 andthe nozzle 3.

The invention further relates to improvements in the temperature controland wiring protection.

It is not usual for wiring on injection-moulding devices to be fullyprotected by metal constructions. It is known that, during transport ofthe injection-moulding device and during assembly of aninjection-moulding device in a mould, damage often occurs to the wiringof the injection-moulding device. The solution has heretofore beensought in better protection of the wiring by means of flexible metalhoses or braided metal hoses. These hoses provide protection in eachcase to five wires; two wires for the heating element, two wires for thethermocouple and one wire for earth. In each case therefore, the wiresfor one zone. The wires themselves are usually coated with Teflon. Aglass-fibre hose impregnated with silicones is often further arrangedround the five wires in the metal hose. In order to prevent theconnections of the wires to the heating elements and thermocouplesbreaking off after a short time, they are often given a robust form.These connections are generally freely accessible and therefore quicklysustain mechanical damage.

The drawbacks hereof are that mechanical damage cannot be prevented withabsolute certainty and that teflon is only resistant up to 260° C. Abovethis is temperature the material becomes soft and the conductor canpenetrate through the insulation. It is noted that process temperaturescan rise to 425° C. A final drawback is that because robust solutionsare chosen the connections take up much space.

These drawbacks are obviated with the measures according to the presentinvention where a sleeve extends over an expansion space in the gate.All wiring and all connection points are concealed from view by a metalconstruction. It is hereby no longer possible for mechanical damage tothe wiring to occur during transport of the injection-moulding deviceand during assembly in the mould. Teflon is replaced by Kapton. This isresistant to higher temperatures. An additional advantage is that theinsulating value of Kapton is very high. The outer diameter of theinsulated wire is hereby considerably smaller. Because wiring andconnection lie inside a metal construction, further protective hoses nolonger have to be arranged.

The advantages hereof are that mechanical damage to wiring andconnections during transport and assembly in the mould is precluded, andthat the space occupied by the wiring is considerably smaller.

It is usual for one heating element or two parallel heating elements tobe included per zone. In the case two are arranged, both are necessaryto effect proper functioning. In an injection-moulding device there areat least four zones, although this number is generally exceeded.Injection-moulding devices with 40 to 50 zones are not unusual. Aninjection-moulding device no longer operates properly if one heatingelement fails. If two fail, the injection-moulding device usually ceasesto function.

A choice is often made for heating elements of robust dimensions. Asalready described above, this is done mainly to reduce mechanicaldamage.

The drawbacks hereof are that the injection-moulding device no longerfunctions if one or a number of heating elements fail, and that thechosen heating elements take up a relatively large amount of space.

Owing to the complete protection of wires and connections it is nolonger necessary to opt for robust heating elements. A choice is nowmade for heating elements of small dimensions. This choice enables themounting of an additional heating element in the same space. Thisprovides the option of switching to the additional heating element whenthe first element fails.

An advantage hereof is that it will be hereby possible for theinjection-moulding device to continue functioning much longer before anyaction is taken to replace faulty heating elements.

It is usual for one thermocouple to be mounted per zone. If onethermocouple fails, the injection-moulding device will no longerfunction properly. If two or more thermocouples fail, theinjection-moulding device ceases to function.

Two thermocouples are mounted per zone. For the same reason as in thecase of heating elements, a choice is made for thermocouples inrelatively small form. The injection-moulding device will hereby remainin operation longer before repairs must be made.

An electronic apparatus is required per heating zone to maintain thetemperature as accurately as possible. Currents which have to besupplied can rise to 16 amps. It is usual at the moment for theseapparatuses to have a limited functionality. They usually regulate thetemperature as independent units. Such an apparatus is sometimes able toreport that the element or the thermocouple has failed. It is sometimesable to report the power consumption. In some cases it is possible tohave the apparatuses communicate with a PC.

A drawback hereof is that is necessary to install the correct controlsoftware per control apparatus. A memory module per unit is required forthis purpose. When the software has to be updated, each unit will haveto be disassembled.

The control software will now be stored in a PC. The control apparatusitself will no longer contain any intelligence. It will be in continuousconnection with the PC. The measured values will be transmitted to thePC. Software is then available here which determines what the controlapparatus must do. These commands are subsequently sent back again tothe control unit.

The advantages hereof are that the control unit can be built in asimpler form and thus more cheaply, and that in the case of a possiblesoftware update only the software on the PC has to be upgraded.

The control apparatus will not only be connected to the main heatingelement and the main thermocouple, but will also be connected to theadditionally mounted heating element and thermocouple. The PC will beprovided with comprehensive software. If for instance a heating elementwere to fail, the control unit will then be able to determine this andpass this information to the PC. The PC can then give the command toswitch on the second heating element.

In addition, the software can monitor all manner of things, such as forinstance energy consumption. Should irregularities occur, these can thenbe reported. It is also possible in this way to determine the degree ofwear of a heating element. It thus becomes possible to predict when anelement will fail.

The advantages hereof are that the injection-moulding device will be inoperation longer without intervention of staff, the reliability of theinjection-moulding device will be greater, and periodic maintenance cannow be planned. There will be less necessity for ad hoc maintenance.

What is claimed is:
 1. An injection-moulding device for injectionmoulding of plastic objects, comprising a mould which defines a mouldcavity, in which mould is provided a flow channel for the at leastpartially liquid plastic, which flow channel extends through a manifoldand a number of nozzles connected to the manifold, wherein the flowchannel contains a number of transverse separating surfaces betweenstructural components, and at least one transverse separating surface isbridged by a sealing element in the flow channel, wherein the sealingelement is provided clampingly on the structural components and whereinthe structural components defining the transverse separating surface areformed by the manifold and a nozzle.
 2. An injection-moulding device forinjection moulding of plastic objects, comprising a mould which definesa mould cavity, in which mould is provided a flow channel for the atleast partially liquid plastic, which flow channel extends through amanifold and a number of nozzles connected to the manifold, wherein theflow channel contains a number of transverse separating surfaces betweenstructural components, and at least one transverse separating surface isbridged by a sealing element in the flow channel, wherein the sealingelement is provided clampingly on the structural components, wherein thesealing element is shrink-fitted into the structural components.
 3. Thedevice as claimed in claim 2, wherein the sealing element is provided onthe structural components with an overmeasure in the dimension in axialdirection.
 4. The device as claimed in claim 1, wherein the sealingelement is formed by a cylindrical bush, wherein the ratio of thediameter of the flow channel, wall thickness of the bush and height ofthe bush equals 22:2:10.
 5. The device as claimed in claim 1, whereinthe structural components are provided with a corresponding recess forthe sealing element for housing of the sealing element.
 6. The device asclaimed in claim 5, wherein the recess has a form and dimension suchthat the passage of the flow channel over the seal remains constant. 7.The device as claimed in claim 1, wherein the sealing element ismanufactured from a metal alloy, for instance a high chromium contentalloy.
 8. An injection-moulding device for injection moulding of plasticobjects, comprising a mould which defines a mould cavity, in which mouldis provided a flow channel for the at least partially liquid plastic,which flow channel extends through a manifold and a number of nozzlesconnected to the manifold, wherein the flow channel contains a number oftransverse separating surfaces between structural components, and atleast one transverse separating surface is bridged by a sealing elementin the flow channel, wherein the sealing element is provided clampinglyon the structural components, wherein an additional seal is providedbetween the structural components which is formed by self-sealingsealing rings which are arranged diametrically relative to the flowchannel in the transverse separating plane.
 9. The device as claimed inclaim 1, wherein the nozzle is mounted on the manifold by means of anumber of, preferably two, and more preferably four, independentlycontrollable connecting elements.
 10. The device as claimed in claim 9,wherein a connecting element is formed by a nut and bolt assembly,wherein the nut is preferably a clamp plate.
 11. The device as claimedin claim 1, wherein an adaptor nozzle is provided between the manifoldand a nozzle, wherein an angular displacement is possible between themanifold and the adaptor nozzle.
 12. The device as claimed in claim 1,wherein the structural components defining the transverse separatingsurface are formed by nozzle parts.
 13. The device as claimed in claim12, wherein two semi-circular clamping plates are provided round thetransverse separating surface for enclosing the outer periphery of thenozzle parts.
 14. The device as claimed in claim 13, wherein the outerperiphery of the nozzle parts is provided with a stepped portion and theclamping plates with a corresponding recess.
 15. The device as claimedin claim 1, wherein the nozzle on the mould cavity runs out onto a gate,wherein the gate comprises an assembly displaceable in longitudinaldirection.
 16. The device as claimed in claim 15, wherein the sleeveextends over an expansion space in the gate.
 17. The device as claimedin claim 1, wherein the device is provided with dual heating elements.18. The device as claimed in claim 1, wherein the device is providedwith dual thermocouples.
 19. An injection-moulding device for injectionmoulding of plastic objects, comprising a mould which defines a mouldcavity, in which mould is provided a flow channel for the at leastpartially liquid plastic, which flow channel extends through a manifoldand a number of nozzles connected to the manifold, wherein the flowchannel contains a number of transverse separating surfaces betweenstructural components, and at least one transverse separating surface isbridged by a sealing element in the flow channel, wherein the sealingelement is provided clampingly on the structural components and whereinthe structural components defining the transverse separating surface areformed by nozzle parts.
 20. The device as claimed in claim 19, whereintwo semi-circular clamping plates are provided round the transverseseparating surface for enclosing the outer periphery of the nozzleparts.
 21. The device as claimed in claim 20, wherein the outerperiphery of the nozzle parts is provided with a stepped portion and theclamping plates with a corresponding recess.
 22. The device as claimedin claim 19, wherein the device is provided with dual heating elements.23. The device as claimed in claim 19, wherein the device is providedwith dual thermocouples.
 24. An injection-moulding device for injectionmoulding of plastic objects, comprising a mould which defines a mouldcavity, in which mould is provided a flow channel for the at leastpartially liquid plastic, which flow channel extends through a manifoldand a number of nozzles connected to the manifold, wherein the flowchannel contains a number of transverse separating surfaces betweenstructural components, and at least one transverse separating surface isbridged by a sealing element in the flow channel, wherein the sealingelement is provided clampingly on the structural components and whereinthe device is provided with at least a pair of heating elements.
 25. Thedevice as claimed in claim 24, wherein at least a pair of heatingelements is located in each structural component.
 26. Aninjection-moulding device for injection moulding of plastic objects,comprising a mould which defines a mould cavity, in which mould isprovided a flow channel for the at least partially liquid plastic, whichflow channel extends through a manifold and a number of nozzlesconnected to the manifold, wherein the flow channel contains a number oftransverse separating surfaces between structural components, and atleast one transverse separating surface is bridged by a sealing elementin the flow channel, wherein the sealing element is provided clampinglyon the structural components and wherein the device is provided with atleast a pair of thermocouples.
 27. The device as claimed in claim 25,wherein at least a pair of thermocouples is located in each structuralcomponent.